code: def test_sobel_zeros():
      A = np.zeros((15, 100))
      assert sobel(A).shape == A.shape
      assert sobel(A).sum() == 0
  
file_path: mahotas/mahotas/tests/test_edge.py
imports: from mahotas.edge import sobel
  import pytest
  import mahotas
  import numpy
label_desc: Use image node_id 2 for calling a global function with example usage: test_sobel_zeros() without return types